.TH std::ranges::max_element 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::ranges::max_element \- std::ranges::max_element

.SH Synopsis
   Defined in header <algorithm>
   Call signature
   template< std::forward_iterator I, std::sentinel_for<I> S, class Proj =
   std::identity,

             std::indirect_strict_weak_order<std::projected<I, Proj>> Comp  \fB(1)\fP (since
   = ranges::less >                                                             C++20)
   constexpr I

       max_element( I first, S last, Comp comp = {}, Proj proj = {} );
   template< ranges::forward_range R, class Proj = std::identity,

             std::indirect_strict_weak_order<
                 std::projected<ranges::iterator_t<R>, Proj>> Comp =        \fB(2)\fP (since
   ranges::less >                                                               C++20)
   constexpr ranges::borrowed_iterator_t<R>

       max_element( R&& r, Comp comp = {}, Proj proj = {} );

   1) Finds the greatest element in the range [first, last).
   2) Same as \fB(1)\fP, but uses r as the source range, as if using ranges::begin(r) as
   first and ranges::end(r) as last.

   The function-like entities described on this page are niebloids, that is:

     * Explicit template argument lists cannot be specified when calling any of them.
     * None of them are visible to argument-dependent lookup.
     * When any of them are found by normal unqualified lookup as the name to the left
       of the function-call operator, argument-dependent lookup is inhibited.

   In practice, they may be implemented as function objects, or with special compiler
   extensions.

.SH Parameters

   first, last - iterator-sentinel pair denoting the range to examine
   r           - the range to examine
   comp        - comparison to apply to the projected elements
   proj        - projection to apply to the elements

.SH Return value

   Iterator to the greatest element in the range [first, last). If several elements in
   the range are equivalent to the greatest element, returns the iterator to the first
   such element. Returns last if the range is empty (i.e. if first == last).

.SH Complexity

   Exactly max(N - 1, 0) comparisons, where N = ranges::distance(first, last).

.SH Possible implementation

struct max_element_fn
{
    template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity,
             std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less>
    constexpr I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
    {
        if (first == last)
            return last;

        auto largest = first;
        while (++first != last)
            if (std::invoke(comp, std::invoke(proj, *largest), std::invoke(proj, *first)))
                largest = first;
        return largest;
    }

    template<ranges::forward_range R, class Proj = std::identity,
             std::indirect_strict_weak_order<
                 std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less>
    constexpr ranges::borrowed_iterator_t<R>
        operator()(R&& r, Comp comp = {}, Proj proj = {}) const
    {
        return (*this)(ranges::begin(r), ranges::end(r), std::ref(comp), std::ref(proj));
    }
};

inline constexpr max_element_fn max_element;

.SH Example


// Run this code

 #include <algorithm>
 #include <cmath>
 #include <iostream>

 int main()
 {
     namespace ranges = std::ranges;

     const auto v = {3, 1, -14, 1, 5, 9, -14, 9};

     auto result = ranges::max_element(v.begin(), v.end());
     std::cout << "Max element at pos " << ranges::distance(v.begin(), result) << '\\n';

     auto abs_compare = [](int a, int b) { return std::abs(a) < std::abs(b); };
     result = ranges::max_element(v, abs_compare);
     std::cout << "Absolute max element at pos "
               << ranges::distance(v.begin(), result) << '\\n';
 }

.SH Output:

 Max element at pos 5
 Absolute max element at pos 2

.SH See also

   ranges::min_element    returns the smallest element in a range
   (C++20)                (niebloid)
   ranges::minmax_element returns the smallest and the largest elements in a range
   (C++20)                (niebloid)
   ranges::max            returns the greater of the given values
   (C++20)                (niebloid)
   max_element            returns the largest element in a range
                          \fI(function template)\fP
